The present disclosure relates to methods and systems of communication between equipment used in subterranean operations. More particularly, the present disclosure relates to optical bi-directional communication between rotating and non-rotating or rotation-varying members of a downhole tool.
During drilling and production operations, it may be necessary to identify certain downhole characteristics, including fluid, formation, cement, and pipe properties, to aid in drilling decisions. Numerous measurement techniques are used, including logging while drilling (LWD), measuring while drilling (MWD), and wireline tests.
LWD tools and methods evaluate multiple parameters, such as formation resistivity to determine the types of minerals and/or fluids that comprise the formation. LWD tools incorporate measurement devices into a bottom hole assembly (BHA) in order to obtain measurements as soon as possible after the well wall is drilled. LWD has thus far been attached to the drill string, for example, in specially adapted drill collars located just above the drill bit. Thus, the sensors incorporated into these LWD tools will typically detect formation properties at a depth only after the drill bit drills past that depth.
In addition, it may be necessary to have elements in the drill string that rotate at different rates from that of the drill string itself, including non-rotating or slowly rotating members or in the opposite direction of the drill string rotation. Such drill string elements are used for creating geostationary orientation platforms such as in rotary steerable tools. Other applications may need a geostationary platform for making measurements of the formation such as rock properties. Some elements may need to be rotated while the drill sting does not rotate to make azimuthal measurements such as formation resistivity anisotropic measurements.
In all these cases, there is a need to communicate data and/or commands between two rotationally variant members of the drill string. These members can be located at any point in the drill string but most commonly are found in the BHA area of the drill string near the distal end of the drill string.
As sensor technology progresses, there is a need to move more and more data from the sensors to memory locations elsewhere in the drill string for later retrieval or further processing. Such data may also be needed in real-time on surface and needs to be transmitted to surface over high data rate telemetry systems such as high speed acoustic channels, EM telemetry, wired drill pipe, fiber optics, EM wave guides, or pipe-in-pipe communication systems. Such data rates can easily be required to be in the thousands to millions of bits per second. As technology improves, we may yet see gigabit volumes of data transference on a routine basis to characterize formations with various sensor technology.
Further, with the advent of laser drilling and pulse power drilling, high electromagnetic pulse energy levels may be present in the BHA during drilling operations with these systems. The communications bus may carry voltages in excess of 10,000 volts or more. In such instances, it is difficult to isolate sensitive electronics from these kinds of electromagnetic pulse (EMP) energies.
While embodiments of this disclosure have been depicted and described and are defined by reference to example embodiments of the disclosure, such references do not imply a limitation on the disclosure, and no such limitation is to be inferred. The subject matter disclosed is capable of considerable modification, alteration, and equivalents in form and function, as will occur to those skilled in the pertinent art and having the benefit of this disclosure. The depicted and described embodiments of this disclosure are examples only, and not exhaustive of the scope of the disclosure.